I'm assuming based on what you're saying, it reaches the POST screen and then freezes with the POST screen up. It never goes to a black or error screen.
The distinction here is whether it's actually completing the POST.
If it freezes on the POST screen, then it's actually not POSTing, it's failing to POST.
If it goes to say a black screen with nothing on it, or an error then it may be POSTing, and failing after the POST.
It's an important distinction.
If it's failing to POST and everything else is correctly connected, and no beep codes are appearing, then it's pointing towards a bad MOBO.